JP2002366103A - Processing for picture data to be supplied to picture display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide technique for improving picture quality by the processing of supplied picture data with respect to a picture display device in which the number of displayable gradation is smaller than that of gradation of original picture data and which has a nonlinear display characteristics. SOLUTION: The technique corrects gradation values of respective pixels by using a lookup table so as to enlarge the gradation distribution of an area where an interval of luminance to be outputted is wide in consideration for the nonlinearity of a picture display device and also to suppress the distribution of an area where an interval of luminance is narrow. Then, colors of these correction values are reduced to the number of display gradation which can be displayed by the picture display device by a distribution type halftone processing. A plurality of lookup tables are prepared in accordance with conditions of temperature or the like affecting to the display characteristics of the picture display device and these lookup tables are changeable in accordance with the conditions.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to the processing of image data supplied to an image display device.

[0002]

2. Description of the Related Art Conventionally, a liquid crystal display (LCD) is provided on an image display section of a portable telephone.
spray) panel is used. The LCD panel displays characters and images of two gradations by changing the transmittance of the liquid crystal by turning on / off a driving voltage to liquid crystal cells arranged in a matrix. In recent years, mobile phones have become multifunctional, and models that can connect to the Internet have appeared. Along with this, a multi-gradation display has been required for an LCD panel of a mobile phone so that more information can be displayed. Further, in recent years, the LCD panel provided in the mobile phone has been colored, and a multi-tone display of a color image has become possible.

By the way, image data read by an input device such as a scanner or a digital camera, or image data designed on a computer is usually used for R,
G and B are 8-bit data (256 gradations). On the other hand, the number of tones that the LCD panel included in the mobile phone can represent for each cell is smaller than the number of tones of the original image data. Therefore, the color reduction processing is performed as follows. It is assumed that the LCD panel can express eight gradations. FIG.
FIG. 4 is an explanatory diagram showing a state in which data of 256 gradations is reduced to 8 gradations. The data of 256 gradations is equally divided into sections corresponding to the number of display gradations of the LCD panel, and the gradation values in each section are sequentially assigned to the display gradation values that can be expressed by the LCD panel, thereby forming 8 gradations. The color is reduced. For example, the display gradation value of a pixel whose input gradation value is 190 is uniquely assigned to 5. Such a color reduction method is called “simple color reduction”.

[0004] Multi-gradation display on an LCD panel is possible by setting the effective drive voltage to the liquid crystal cell in a stepwise manner and controlling the transmittance of the liquid crystal in a stepwise manner. This LC
The following two types of D-panel drive voltage settings are known. FIG. 21 is an explanatory diagram showing a voltage-transmittance characteristic (VT characteristic) of the LCD panel, that is, a transmittance of the liquid crystal with respect to an effective driving voltage.

A first setting is a setting (FIG. 21A) in which intervals between transmittances are equal. It is known that the VT characteristic of an LCD panel is non-linear. For this reason, the effective drive voltage is controlled by pulse width modulation so that the intervals of the transmittance become uniform. The effective drive voltage corresponds to the display gradation value that can be expressed by the LCD panel, and the relationship between the display gradation value and the output brightness becomes linear.

The second setting is a setting (FIG. 21B) in which the effective driving voltages are at equal intervals. One screen is constituted by using a plurality of frames, and the driving voltage is ON / OFF controlled on a frame basis for each pixel to enable multi-gradation expression. However, the interval of the transmittance of the liquid crystal, that is, the interval of the lightness that can be expressed by the LCD panel varies widely, and the relationship between the display gradation value that can be expressed by the LCD panel and the output lightness becomes non-linear. For example, when driving an LCD panel in the range of the effective driving voltage shown in FIG. 21B, the lightness interval that can be expressed in the halftone region is wide, and the interval in the low gradation region and the high gradation region is narrow. Become.

As described above, a pulse width modulation type LCD panel has conventionally been mainly used in portable telephones in consideration of color reproducibility.

[0008]

However, in a portable telephone having a small battery capacity, a pulse width modulation type L is used.
Since the power consumption of the CD panel is large, the power consumption cannot be overlooked from the viewpoint of battery life and energy saving. Therefore, a frame-thinning type LCD panel with low power consumption has been adopted for a mobile phone.

As described above, the LCD panel of the frame thinning system has a non-linear display characteristic, so that the image quality is seriously degraded. In particular, image quality degradation was remarkable in a natural image having a large amount of image data in a halftone area. For example, when displaying an image of “sky” or “human skin” in which the gradation value changes continuously, the same brightness (display scale) is used in the region where the gradation values of adjacent pixels are close in the original image data. (Tone value). At the same time, since there is a large difference in brightness even if the display gradation value is different by one step, a pseudo contour occurs at the boundary between the two. It is difficult to improve these image quality deteriorations in terms of hardware.

[0010] Usually, a liquid crystal display device having an LCD panel is provided with an electronic volume for adjusting display contrast, and the electronic volumes are individually adjusted so that the contrast of the LCD panel is maximized. FIG.
FIG. 4 is an explanatory diagram illustrating adjustment of display contrast of an LCD panel by an electronic volume. For example, when the setting of the electronic volume is “1”, when the drive voltage of the LCD panel is on and off, the voltages are V1on and V1on, respectively.
1off, and the transmittances are T1on and T1o, respectively.
ff. When the setting of the electronic volume is “2”, when the driving voltage of the LCD panel is ON and OFF, the voltage is as follows:
V2on and V2off, respectively, and the transmittances are T2on and T2off, respectively. And between these, V1on / V1off = V2on / V2off =
There is a certain relationship. T1on-T1off, T2on
−T2off corresponds to the contrast.

However, the contrast of the LCD panel changes depending on the use environment (temperature and brightness) and the setting (ON / OFF of the backlight). For example, due to the temperature characteristics of the LCD panel, when the use environment is low temperature, the transmittance of the LCD panel is reduced, and the contrast is weakened.
When the temperature is high, the transmittance of the LCD panel increases, and the contrast of the screen increases. Such a change in contrast may cause deterioration in image quality.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and an image display apparatus having a non-linear display characteristic in which the number of expressible gradations is smaller than the number of gradations of original image data. It is an object of the present invention to provide a technique for improving the image quality by processing the image data supplied to the apparatus.

[0013]

Means for Solving the Problems and Their Functions and Effects In order to solve at least a part of the above-mentioned problems, the present invention employs the following constitution. A first image processing apparatus of the present invention is an image processing apparatus that performs predetermined image processing on image data and generates data to be supplied to an image display apparatus, wherein the image display apparatus is a frame thinning method. A liquid crystal display device that performs gradation display by using a display device and the number of display gradations that can be displayed in pixel units is smaller than the number of gradations of the image data. A color reduction processing unit configured to set a display gradation value that can be displayed by the liquid crystal display device for each pixel based on a gradation value of the image data, wherein the color reduction processing unit assigns the display gradation value to the display gradation value. The gist is that the setting is performed so that the range of the gradation value to be obtained is at least one of the high gradation and the low gradation, and is narrower than the halftone.

As described above, normally, when performing color reduction processing, the gradation values of input image data are divided at equal intervals and assigned to display gradation values that can be expressed by the image display device. When an image is displayed on an image display device having linear display characteristics, the image display device outputs lightness with respect to the display gradation value at equal intervals, so that ideal gradation display with good color balance is achieved. realizable. However, the image is displayed on a liquid crystal display device that performs gradation display by a frame thinning method and has a smaller number of display gradations that can be displayed in a pixel unit than the number of gradations of image data, that is, an image display device having nonlinear display characteristics. Is displayed, the output lightness is biased, so that an ideal gradation display cannot be performed. Then, by setting the electronic volume shown in FIG. 22, at least one of the low gradation and the high gradation, the expressible lightness interval is narrower than the halftone. According to the present invention, in the color reduction processing unit, the display gradation value is set such that the range of the gradation value assigned to the display gradation value is at least one of the high gradation and the low gradation and narrower than the halftone. . By doing so, it is possible to approach an ideal gradation display. Note that the setting is preferably set so that the same width as the brightness interval output by the image display device with respect to the display gradation value occurs.

A second image processing apparatus according to the present invention is an image processing apparatus which performs predetermined image processing on image data to be displayed on an image display device and generates data to be supplied to the image display device. In the image display device, the number of display gradations that can be expressed for each pixel is smaller than the number of gradations of the image data, and the brightness output for the display gradation value is stepwise. A device having non-linear display characteristics having wide and narrow intervals, and considering a non-linearity of the display characteristics, a gradation distribution corresponding to a region having a wide interval in a gradation distribution of input image data. And an image data correction unit that performs a gradation correction for suppressing a gradation distribution corresponding to the area where the interval is small, and divides a gradation range of the correction value into a predetermined number of sections, and Set the correction value to the specified Wherein the subject matter in that it comprises a color reduction process unit that performs subtractive color processing by assigning to the display tone value according to.

According to the second image processing apparatus of the present invention, in consideration of the non-linear display characteristics of the image display device, the gradation distribution corresponding to the region having the wide interval is obtained in the gradation distribution of the input image data. A gradation correction is performed to suppress the gradation distribution corresponding to the area where the interval is small as the size increases, and a color reduction process is performed in which the correction value is assigned to a display gradation value according to a predetermined rule. Here, “increase the gradation distribution” means to increase the number of pixels having a gradation value in a predetermined area. Further, “suppressing the gradation distribution” means reducing the number of pixels having a gradation value in a predetermined area.

This image processing is equivalent to changing the range of the input gradation value assigned to each display gradation value. Therefore, by doing so, it is possible to approach an ideal gradation display, as in the first image processing apparatus of the present invention. Further, by separating the image data correction unit and the color reduction processing unit, each unit can be separately designed. Therefore, when the display characteristics of the image display device change, it is only necessary to change the image data correction unit, and there is an advantage that the image data can be flexibly handled.

In the image processing apparatus, the predetermined number of sections is preferably a section obtained by dividing the gradation range of the correction value into an equal range. In particular, it is preferable to divide into sections for every power of two.

This makes it possible to perform the color reduction processing evenly in each section. The “equivalent range” does not need to be strictly equal. Further, if the image processing apparatus is configured by using a computer, the operation speed can be increased and the speed of image processing can be increased if the image processing apparatus is configured using a computer.

A third image processing apparatus according to the present invention is an image processing apparatus that performs predetermined image processing on image data to be displayed on an image display device and generates data to be supplied to the image display device. In the image display device, the number of display gradations that can be expressed for each pixel is smaller than the number of gradations of the image data, and the brightness output for the display gradation value is stepwise. A device having a non-linear display characteristic having a wide and narrow interval, wherein a gradation range of the gradation value of the image data is divided into sections having a width corresponding to the display characteristic, and the gradation value in the section is divided. The present invention is characterized in that a color reduction processing unit that performs a color reduction process by assigning to the display gradation value according to a predetermined rule is provided.

According to the present invention, the image is divided into sections having wide and narrow areas according to the display characteristics of the image display device, and the color reduction processing for assigning to the display gradation values in accordance with a predetermined rule is performed. As in the case of the device, it is possible to approximate an ideal gradation display.

In the first to third image processing apparatuses according to the present invention, the color reduction processing section may perform color reduction by distributed halftone processing.

Here, the “dispersion type halftone process” is a halftone process in which pixels having the same display gradation value are dispersed after the color reduction process so as not to be clustered. As this kind of halftone processing, a known technique such as a dither method or an error diffusion method can be applied.

By applying distributed halftone processing as color reduction processing, pixels having the same brightness can be dispersed within a predetermined area, so that the occurrence of false contours is suppressed and the image quality of the displayed image is improved. be able to.

In the image processing apparatus according to the present invention, the image display device may be a liquid crystal display device used for a portable telephone and performing a gradation display by a frame thinning method.

In general, a liquid crystal display device that performs grayscale expression by a frame thinning method has a stepwise brightness output with respect to a displayable grayscale value that can be expressed due to its driving method, and a low level. At least one of the tone region and the high gradation region has a non-linear display characteristic in which the interval is wide and narrow. Since this liquid crystal display device is superior in power consumption to a liquid crystal display device driven by pulse width modulation, it may be mounted on a mobile phone having a small battery capacity. INDUSTRIAL APPLICABILITY The present invention can be applied to image processing of image data to be supplied to a liquid crystal display device having a small number of display gradations, which is used in a mobile phone and performs gradation display by a frame thinning method.

In the second image processing apparatus according to the present invention, the image data correction unit further suppresses a gradation distribution in a halftone region and increases a distribution in a low gradation region and a high gradation region. May be applied. Further, the first image processing apparatus may include the image data correction unit.

By doing so, the contrast of the displayed image can be increased. Note that when the area where the brightness interval outputted by the image display device is wide is the halftone area and the narrow areas are the low gradation area and the high gradation area, the gradation correction described above is performed. This is a correction that is contrary to the correction. Therefore, in this case, the gradation correction is performed to such an extent that the effect of the previous gradation correction is not impaired. Further, in the case of performing the distributed halftone processing in the color reduction processing unit of the image processing apparatus, the frequency of adjacent pixels having a large difference in brightness in the halftone can be reduced, so that the display quality can be improved. it can.

In the second image processing apparatus according to the present invention, the image data correction unit includes a storage unit for storing a relationship between a gradation value of the input image data and a corrected gradation value. The gradation value may be corrected by referring to a storage unit. The first image processing apparatus may include the image data correction unit.

The relationship between the tone value of the input image data and the tone value of the corrected image data is stored in advance, and the image data can be easily corrected by referring to the stored relationship. . Note that the storage means may be a so-called lookup table, or may perform a correction operation using a predetermined function.

In the above-mentioned image processing apparatus, a plurality of storage means are prepared according to conditions affecting display characteristics of the image display device, and a storage means changing section for changing the storage means according to the conditions. It is preferable to provide

For example, the condition may be a temperature of an environment in which the image display device is used.

The display characteristics may change depending on the temperature of the environment in which the image display device is used. In such a case, the image quality of the display image can be improved by appropriately changing the storage unit according to the environmental temperature and performing the gradation correction of the image data. As for the environmental temperature, the detection result detected by the temperature sensor may be automatically input, or may be manually input.

[0034] The condition may be a brightness of an environment in which the image display device is used.

The display characteristics may change depending on the brightness of the environment in which the image display device is used. Even in such a case, the image quality of the display image can be improved by appropriately changing the storage unit according to the brightness of the usage environment and performing the gradation correction of the image data. The brightness is
The detection result detected by the optical sensor may be automatically input, or may be input manually.

Further, when the image display device is a liquid crystal display device having a backlight, the condition may be the brightness of the backlight.

The display characteristics of the liquid crystal display device change depending on the brightness of the backlight. Therefore, the image quality of the display image can be improved by changing the storage means in accordance with the brightness and on / off of the backlight and performing the gradation correction of the image data.

Further, the condition may be a set value of a contrast adjuster for adjusting a display contrast of the image display device. An example of the contrast adjuster is an electronic volume.

The display characteristics of the image display device change depending on the set value of the contrast adjuster. Therefore, the image quality of the displayed image can be improved by changing the storage means according to the setting value of the contrast adjuster and performing the gradation correction of the image data.

According to the fourth image processing apparatus of the present invention, the number of display gradations that can be expressed for each pixel is smaller than the number of gradations of the image data, and the brightness output for the display gradation value. Is an image processing apparatus for performing predetermined gradation correction on image data to be displayed on an image display device having a non-linear display characteristic in which the intervals are wide and narrow. A first storage unit that stores a relationship between the tonal value and the brightness in association with a predetermined parameter value;
A second storage unit for storing a desired relationship preset for the tone value and the lightness, acquiring the parameter value, and based on the relationship specified by the parameter value and the desired relationship. A data generating unit that generates data representing a relationship between a tone value of the image data and a tone value of the corrected image data so as to compensate for a difference between the two.
An image data correction unit that corrects a gradation value of the input image data with reference to the generated data.

In this way, data representing the relationship between the necessary gradation values of the input image data and the gradation values of the corrected image data is generated according to the predetermined parameter values, and Gradation correction can be performed. As a result, the quality of the displayed image can be improved. In addition,
The “predetermined parameters” include parameters that affect the display characteristics of the image display device, such as the temperature and brightness of the environment in which the image display device is used.

In the above description, the case where the display characteristics of the image display device are non-linear has been exemplified. The application of the tone correction in the present invention is not necessarily limited to an image display device having non-linear display characteristics. A fifth image processing apparatus according to the present invention configured from such a viewpoint performs an image processing to be performed on image data to be displayed on an image display apparatus, and generates data to be supplied to the image display apparatus. A storage unit for storing in advance a relationship set based on display characteristics of the image display device with respect to tone values before and after tone correction, and performing tone correction of the image data based on the relationship. The gist is to include an image data correction unit and a color reduction processing unit that reduces the corrected image data to the number of gradations that can be displayed on the image display device.

As in the image processing apparatus described above,
In the fifth image processing apparatus, it is desirable that the color reduction processing unit performs distributed halftone processing.

The gist of the fifth image processing apparatus is that even if the display characteristics of the image display device are linear, gradation correction is performed according to the display characteristics. The display characteristics considered in the fifth image processing apparatus include, for example, a bias in overall brightness, an increase in brightness with respect to an increase in display gradation value, and the number of displayable gradations.

The "relationship" to be stored in the storage means is set by analysis or experiment in consideration of these characteristics. This relationship does not need to be one, and a plurality may be prepared.

For example, in the fifth image processing apparatus, a plurality of storage means are prepared according to conditions which affect the display characteristics of the image display device, and the storage means may be changed according to these conditions. Good. In this case, appropriate gradation correction can be realized by properly using various relationships according to conditions.

Further, according to the present invention, the number of display gradations that can be expressed for each pixel is smaller than the number of gradations of image data, and
A predetermined gradation correction is performed on image data to be displayed on an image display device having a non-linear display characteristic in which the brightness output for the display gradation value is stepwise and the interval is wide and narrow. (A) specifying a relationship between a tone value of the image data and the brightness; and (b) determining a relationship between a desired tone value and the brightness. Setting a relationship, and (c) based on the relationship specified in the step (a) and the relationship set in the step (b), so as to compensate for a difference between the two. Generating a data representing the relationship between the tone value of the image data input to the processing device and the tone value of the corrected image data.

By doing so, it is possible to generate data for gradation correction used in the above-described fourth image processing apparatus.

The present invention can be configured as an invention of an image processing method in addition to the configuration as the image processing apparatus and the method of generating data used for gradation correction. Further, the present invention can be implemented in various forms such as a computer program for realizing the above, data provided for the program, a recording medium on which the program is recorded, a data signal including the program and embodied in a carrier wave. . In each embodiment, the various additional elements described above can be applied.

When the present invention is configured as a computer program or a recording medium on which the program is recorded, the present invention may be configured as an entire program for driving an image processing apparatus, or only a portion that performs the functions of the present invention may be configured. It may be configured. Examples of the recording medium include a flexible disk, a CD-ROM, a magneto-optical disk, an IC card, a ROM cartridge, a punched card, a printed matter on which a code such as a barcode is printed, and an internal storage device of a computer (a memory such as a RAM or a ROM). )
Also, various computer-readable media such as an external storage device can be used.

[0051]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below in the following order based on an embodiment in which the present invention is applied to a portable telephone. A. Configuration of mobile phone: B. Image processing: Modification of the first embodiment: Second embodiment: Third Embodiment F. Third Embodiment Fourth Embodiment G. Fifth embodiment: Modification:

A. FIG. 1 shows a mobile phone 1 having an image processing apparatus according to a first embodiment of the present invention.
FIG. 3 is a block diagram showing a configuration of a 0. The mobile phone 10
A color LCD panel 20 as an image display unit;
And a system unit 60 having U, ROM, RAM, and the like. The mobile phone 10 is connected to the server SV via the external network TN, so that the color LC
Image data to be displayed on the D panel 20 can be downloaded.

The color LCD panel 20 includes a glass substrate,
It has an RGB color filter, a transparent electrode, a polarizing plate, a backlight, and an LCD drive circuit. The color LCD panel 20 according to the present embodiment has three bits of R (red),
The LCD driving circuit is designed to display 256 colors of (green) 3 bits and B (blue) 2 bits.

The color LCD panel 20 of this embodiment is
Uses STN type liquid crystal and is driven by a passive matrix driving method. A low power consumption type driving circuit for performing frame thinning-out gradation display is adopted, and the effective driving voltages are set at equal intervals (FIG. 21).
(B)). For this reason, the color LCD panel 20
In the halftone region, displayable lightness intervals are wide, and in the low gradation region and the high gradation region, displayable lightness intervals are narrow.

The system unit 60 includes the application program 30, the browser 40, the image processing module 5,
0. The application program 30 includes a PIM (Personal In) for the user to manage personal level information (address book, schedule, etc.).
software, such as an information manager (formation manager), e-mail, and an incoming call waiting screen. The browser 40 is software for displaying data downloaded from the server SV in a viewable manner.

The image processing module 50 includes the image processing unit 5
2 and an LCD driver 56, and a color LCD
R for controlling the driving of each liquid crystal cell of panel 20
(Red), G (green), and B (blue) gradation signals and timing signals are generated. The image processing unit 52 includes a resolution conversion unit 53
, An image data correction unit 54, a gradation value correction table LUT referred to by the image data correction unit 54, and a halftone processing unit 55. The LCD driver 56 includes an electronic volume 58
, Whereby the display contrast of the color LCD panel 20 can be adjusted. However, the adjustment of the contrast of the color LCD panel 20 by the electronic volume 58 has been adjusted so that the contrast becomes maximum when the mobile phone 10 is shipped from the factory.

The resolution converter 53 converts the resolution of the color image data handled by the application program 30 and the browser 40 into a resolution that the LCD driver 56 can handle. The image data correction unit 54 corrects the gradation value of the image data with reference to the gradation value correction table LUT storing the relationship between the gradation value of the input image data and the corrected gradation value. I do. The gradation value correction table LUT is set in advance according to the display characteristics of the color LCD panel 20. The halftone processing unit 55 performs a halftone process on the image data corrected by the image data correction unit 54.

B. Image Processing: FIG. 2 is a flowchart of an image processing routine performed by the image processing module 50. This is a process executed by the CPU in the system unit 60. When this process is started, first, image data is input (step S100). In this embodiment, the file format of the image data is GIF, and the color of each pixel is represented by an 8-bit (256 colors) palette index color. Prior to the input of the GIF file, a color table indicating the correspondence between the palette index colors and the gradation values of R, G, and B of 8 bits (total of 24 bits) is input and stored in the RAM.

Next, each 8-bit image data is converted into a 24-bit (8 bits each for R, G, B) RGB color format (step S110). FIG. 3 is an explanatory diagram showing a color table for converting an 8-bit palette index color into a 24-bit RGB color format. As described above, the color table differs depending on the input image data. According to this color table, an 8-bit palette index color is converted to a 24-bit R color.
It can be converted to GB color format.

Next, the resolution is converted so that it can be displayed on the color LCD panel 20 (step S120).

Next, it is determined whether or not the input image is a natural image (step S130). This determination is made based on the number of colors used in the image. If the number of colors is smaller than the predetermined value, it is determined that the image is not a natural image, and the color is simply reduced (step S160), and the process exits from this routine. If the number of colors is equal to or more than the predetermined number, it is determined that the image is a natural image and the following processing is performed.

If it is determined in step S130 that the input image is a natural image, a gradation value correction table LUT described later is applied to each 24-bit image data.
To correct the gradation value. (Step S14
0). The gradation value correction table LUT is a one-dimensional lookup table prepared for each of R, G, and B.

The correction of the gradation value in step S140 is performed on the input image data by using a tone curve described below. FIG. 4 is an explanatory diagram showing a tone curve representing the relationship between the tone value DXR of the input image data for R (red) and the tone value DXr of the corrected image data. The solid line La is the tone curve. For simplicity of explanation, 25 for input values of 256 gradations
An image display device having nonlinear display characteristics capable of outputting lightness of six gradations will be considered. Note that the input gradation value D
The relationship between XR and the brightness output by the image display device is also shown. An alternate long and short dash line Lb indicates ideal display characteristics. “Ideal display characteristics” means display characteristics in which the relationship between a display gradation value (here, an input value) and brightness has linearity. A chain line Lc indicates a non-linear display characteristic of the image display device.

This tone curve has the meaning of compensating for the non-linear display characteristics of the image display device. For example, ideally, the brightness Lm1 is output for the input value DXR = 64. However, the image display device outputs the lightness Lm2 due to the non-linear display characteristics indicated by the chain line Lc. As shown in the figure, the input value DXR = 80 needs to be input in order for the image display device to output the lightness Lm1. Therefore, the input value DXR = 64 is corrected to the correction value DXr = 80. Correction of such a gradation value is performed by using a color L whose displayable gradation number is smaller than the gradation number of the image data.
The present invention is also applicable to data supplied to the CD panel 20.

The tone curve can be set arbitrarily according to the display characteristics of the color LCD panel 20. A tone curve may be set in consideration of the gamma characteristics of the color LCD panel 20 and the visibility of human eyes. G (green),
Similarly, for B (blue), a tone curve representing the relationship between the tone value of the input image data and the tone value of the corrected image data is set.

FIG. 5 shows a tone value correction table L in which tone curves for R (red) shown in FIG. 4 are shown in a table.
UT. This gradation value correction table LUT is stored in the ROM in the image processing module 50 (see FIG. 1). The gradation value correction tables LUT for G (green) and B (blue) are also stored in the ROM. By referring to this table, it is possible to easily correct the gradation value.

After the gradation value is corrected, a halftone process is performed (step S150). By this processing, R, G, and B data of 8 bits (256 gradations) are converted into 3 bits (8 gradations) for R and G, and B for B, so that the drive circuit of the color LCD panel 20 can control the drive. Each color is reduced to two bits (four gradations). This process is performed for each of the RGB components. The well-known dither method and error diffusion method can be applied to the halftone processing.
In this embodiment, the dither method is applied.

FIG. 6 is a flowchart of a halftone processing routine according to this embodiment. FIG. 6 shows the case of R (red) and G (green) for reducing the gradation data of 256 gradations to 8 gradations. In this embodiment, the dither method is applied to the halftone processing, and one 4 × 4 dither matrix in which threshold values TH of 0 to 15 are arranged is prepared. In addition to thresholds TH of the dither matrix, thresholds TH1 to TH6 for assigning data of 256 gradations to 8 gradations
(0 <TH1 <TH2 <... <TH6 <255) are prepared. The thresholds TH1 to TH6 can be set arbitrarily. In the present embodiment, the threshold values TH1 to TH6 are set at substantially equal intervals so that the data of the sections divided by these are processed almost equally (TH1 = 3).
6, TH2 = 73, TH3 = 109, TH4 = 146,
TH5 = 182, TH6 = 219).

FIG. 7 is an explanatory diagram showing an example of the dither matrix. The gradation value after color reduction is determined depending on whether or not data DX ′ described later is larger than a threshold value TH of the dither matrix. In this embodiment, a 4 × 4 dither matrix is used as an example, but the present invention is not limited to this, and dither matrices of different sizes may be used.

When the halftone process is started, first,
The correction data DX corrected in step S140 of FIG. 2 is input (step S200).

Next, it is determined whether or not the correction data DX is less than the threshold value TH1 (step S210). If the correction data DX is less than the threshold value TH1, the value in the range of 0 to TH1 is 0 to 15 which is the range of the threshold value TH of the dither matrix.
(Step S212). For example, assuming that the correction data DX = 24 and the threshold value TH1 = 36, DX ′ becomes
DX ′ = 15 · DX / TH1
X ′ = 10. Next, it is determined whether or not the value DX ′ normalized in step S212 is larger than the threshold value TH of the dither matrix (step S214). If DX 'is equal to or smaller than the threshold TH, the display gradation value CDX is set to 0 (step S216). If DX' is larger than the threshold TH, the display gradation value CDX is set to 1 (step S226).

In step S210, the correction data D
If X is equal to or greater than TH1, it is determined whether or not X is less than the threshold value TH2 (step S220). If the correction data DX is less than the threshold value TH2, the correction is performed by interpolation so that the value in the range of TH1 to TH2 falls within the range of 0 to 15 which is the range of the threshold value TH of the dither matrix (step S222). At this time, DX ′ is DX ′ = 15 · (DX−TH1) /
(TH2-TH1). Next, step S
It is determined whether the value DX ′ corrected in 222 is larger than the threshold value TH of the dither matrix (step S22)
4). If DX ′ is equal to or less than the threshold value TH, the display gradation value CD
X = 1 (step S226), and if larger than the threshold value TH, the display gradation value CDX = 2 (step S23).
6). Hereinafter, the display gradation value CDX is similarly determined.

Then, step S200 is performed for all pixels.
When the process from to S278 is completed, the halftone process is completed (step S280). If the processing has not been completed for all the pixels, the above processing is repeated until the processing is completed.

When the halftone processing ends, the image processing routine shown in FIG. 2 ends, and an image is displayed on the color LCD panel according to the display gradation value CDX.

Halftone processing is similarly performed for B (blue), which reduces the gradation data of 256 gradations to 4 gradations. In the present embodiment, the dither method described above is applied to the halftone processing as an example, but another method such as an error diffusion method may be applied.

According to the above-described embodiment, since the gradation correction for compensating the non-linearity of the color LCD panel 20 is performed, it is possible to approximate an ideal image display.

FIGS. 8 and 9 are explanatory diagrams showing the effect of the tone correction of the present embodiment. In order to facilitate understanding, it is assumed that simple color reduction is performed after gradation correction. It is also assumed that the lightness interval displayed for the display gradation value is narrower in the low gradation and high gradation regions than in the halftone region. First, a display in the case where the gradation correction is not performed according to the present embodiment will be described. The lower part of FIG. 8A shows a histogram representing the relationship between the input gradation value and the frequency (the number of pixels). FIG.
(A) The upper row shows a histogram indicating the relationship between the display gradation value after gradation correction and simple color reduction and the frequency and brightness thereof.

As shown in the lower part of FIG. 8A, it is assumed that data is input in which n pixels each having 256 gradation values exist. This data corresponds to, for example, a gradation pattern in which the gradation value changes from 0 to 255. FIG. 8B shows an example of a gradation pattern. This pattern corresponds to the color LC of the mobile phone 10.
The patch is displayed on the D panel 20 as a rectangular patch. The brightness is
In the figure, it is assumed to be uniform in the y direction and to change (increase) in the x direction. When the simple color reduction shown in FIG. 20 is performed on this data, as shown in FIG. 8A, the pixels in the sections ab, bc, cd,... Are assigned to the display gradation values CDX = 1, 2, 3,.... Assuming that each section includes N pixels,
The frequency of each display gradation after the color reduction is N. In the case of an ideal 8-gradation display, as shown by a thick broken line in the upper part, each display gradation value is displayed with lightness at equal intervals. On the other hand, in a display having non-linearity as in the present embodiment, brightness intervals are displayed unequally as shown by a thick solid line. Despite the bias in the brightness displayed at each display gradation value,
By assigning a certain frequency N, in this embodiment, the brightness displayed as a whole deviates from the ideal state.

The difference in the brightness is calculated in the low gradation section bc.
Will be described as an example. The section bc corresponds to the area A having a constant width in the pattern shown in FIG. FIG.
(B) Above, the change in brightness in the area A is illustrated by a graph. With the linear change of the gradation value, in the area A,
The brightness to be displayed changes as shown by the straight line L.
At this time, the brightness to be displayed in the entire region corresponds to the hatched area in the figure.

The brightness in the case of displaying at eight gradations is also shown in the figure. As shown in FIG. 8A, the pixels in the section bc are assigned to a constant display gradation value CDX = 2. Therefore, the brightness in the case of performing the 8-gradation display is constant in the region A. The lightness at the ideal display gradation is indicated by a straight line LA2, and the lightness at the display gradation having nonlinearity is indicated by a straight line LA1.

In an ideal display gradation (broken line), the brightness corresponding to the display gradation value CDX = 2 is set to an intermediate value in the section bc. At this time, the brightness displayed in the entire region A, that is, the area between the x axis and the straight line LA2 is equal to the hatched area. This means that in the ideal display gradation, appropriate brightness display is performed in the entire area A.

On the other hand, display gradation having non-linearity (solid line)
Then, the brightness corresponding to the display gradation value CDX = 2 is calculated in the section b
Lower than the median value of -c. Therefore, the area between the x-axis and the line LA2 is smaller than the hatched area.
This means that the brightness displayed in the entire area A is darker than the appropriate value. FIG. 8 exemplifies a lightness shift at a low gradation. At high gradation, the same principle
A shift occurs in which the brightness becomes higher than the appropriate value.

Next, a display when gradation correction using the tone curve of the present embodiment is performed will be described. In this case, as shown in the lower and middle parts of FIG.
1, the values of the sections b1-c1, the sections c1-d1,... Are subjected to gradation correction to the values of the corrected gradation values of the sections ab, bc, section cd,. Then, as shown in the middle and upper parts of FIG. 9, the sections ab, bc,
The pixels in the section cd are the display gradation values CDX = 1, 2, 3,.
Assigned to. Note that the frequency of the corrected gradation value in the middle part of FIG. 9 is illustrated as being constant in each section for convenience.

Sections a-b1 and sections b1-c of input tone values
1. Focus on the section c1-d1. In the gradation correction using the tone curve shown in FIG. 4, correction is performed to increase the gradation value in the low gradation region. For example, the input gradation value b1 is corrected to a correction gradation value b larger than b1. Similarly, the value in the section a-b1 of the input gradation value is the section a-b of the correction gradation value.
It is corrected to the value of Since the section a-b1 of the input tone value is narrower than the section ab, the total number of pixels N1 in the section ab of the corrected tone value is equal to the total number of pixels in the section ab of the input tone value. It is less than the number N. In the gradation correction using the tone curve shown in FIG. 4, since the correction for increasing the distribution of the halftone is performed, the value in the section b1-c1 of the input gradation value is smaller than the correction gradation value smaller than that. The value is corrected to the value in the section bc, and the total number of pixels N2 in the section bc of the corrected gradation value is larger than the total number N of pixels in the section bc of the input gradation value. Furthermore, the value in the section c1-d1 of the input tone value wider than the section b1-c1 is corrected to the value in the section cd of the correction tone value,
The total number of pixels N3 in the section c1-d1 is larger than N2. The pixels in each section are provided with a display gradation value CD.
X = 1, 2, 3 are assigned. At this time, the pixels in the same input gradation value range A as shown in FIG. 8 are assigned to the display gradation values CDX = 2 and CDX = 3, and are displayed with both display gradation values. Since the lightness displayed at the display gradation value CDX = 3 is brighter than the lightness displayed at the display gradation value CDX = 2, the overall lightness of the range A displayed on the color LCD panel 20 is the gradation. Brighter than when no correction is performed. In this way, it is possible to approach an ideal image display.

In the above description, the case where the halftone processing is not performed has been described. However, the effect of gradation correction can be similarly understood when the halftone processing is performed.

In this embodiment, since the halftone processing by the dither method is applied to the color reduction processing, the display gradation value CD
Pixels with the same X can be distributed. As a result, it is possible to suppress the false contour and improve the image quality of the display image.

In this embodiment, the tone curve shown in FIG. 4 and the gradation value correction table LUT shown in FIG.
Can be arbitrarily set according to the display characteristics of the color LCD panel 20. Therefore, it is possible to easily change the color LCD panel 20 and adjust the image quality in terms of software.

C. Modification of First Embodiment: FIG.
Mobile phone 10 provided with image processing device of modified example of embodiment
FIG. 2 is a block diagram showing a configuration of A. Except for the matters described below, the second embodiment is the same as the first embodiment. Mobile phone 10A
Is provided with a color LCD panel 20 as an image display unit and a system unit 60A. The system unit 60A
An application program 30, a browser 40,
An image processing module 50A is provided. The image processing module 50A includes an image processing unit 52A and an LCD driver 56. The image processing unit 52A includes a resolution conversion unit 53, a first image data correction unit 541, a second image data correction unit 542, and a halftone processing unit 55. In addition, a first gradation value correction table and a second gradation value correction table that are referred to by the first image data correction unit 541 and the second image data correction unit 542, respectively, are also provided. The first image data correction unit 541 and the first gradation value correction table correspond to the image data correction unit 5 of the first embodiment, respectively.
4 and the same as the gradation value correction table LUT.

The second image data correction unit 542 performs gradation correction on the first correction value corrected by the first image data correction unit 541. Then, the halftone processing unit 55
A halftone process is performed on the second correction value. That is, the second tone correction performed by the second image data correction unit 542 is a process performed between step S140 and step S150 in FIG.

FIG. 11 shows a tone curve representing the relationship between the input first correction value DXr and the second correction value DXr 'for R (red) recorded in the second gradation value correction table. FIG. The solid line La1 is the tone curve. For example, for a pixel with the first correction value DXr = 64, the second correction value DXr ′ =
52. When the tone curve is set as shown by the dashed line La2, no gradation correction is performed. In a region where the first correction value DXr is smaller than p, D
It is corrected to DXr 'smaller than Xr. On the other hand, in a region where the first correction value DXr is larger than p, the correction is made to DXr ′ larger than DXr.

The contrast of the displayed image can be increased by such second gradation correction. In addition, the frequency of adjacent pixels having a large difference in brightness in halftone can be reduced by halftone processing, so that display quality can be improved. Note that the order of the first gradation correction and the second gradation correction may be reversed.
Further, one tone correction may be performed using a tone curve obtained by combining a tone curve used for the first tone correction and a tone curve used for the second tone correction.

D. FIG. 12 shows a second embodiment of the present invention.
Mobile phone 10B provided with an image processing device as an embodiment
FIG. 3 is a block diagram showing the configuration of FIG. Except for matters described below, the configuration is the same as that of the first embodiment. Mobile phone 10
B is a color LCD panel 20B as an image display unit
And a system unit 60B. Mobile phone 10
B color LCD panel 20B includes a temperature sensor 70,
An optical sensor 80 is provided. The temperature sensor 70 detects the temperature of the environment where the color LCD panel is used. The optical sensor 80 detects the brightness of the environment where the color LCD panel 20B is used.

[0093] The system section 60B includes the application program 30, the browser 40, and the image processing module 50B. The image processing module 50B
An image processing unit 52B and an LCD driver 56B are provided. The image processing unit 52B includes a resolution conversion unit 53, an image data correction unit 54, a plurality of gradation value correction tables LUT referred to by this, a table change unit 57, and a halftone processing unit 55.

The tone value correction table LUT is a color LC
Multiple use environments (temperature and brightness) of the D panel 20B
It has multiple lookup tables for use underneath. FIG. 13 is an explanatory diagram showing a map representing the relationship between the temperature and brightness of the environment using the color LCD panel and the lookup table used. As shown in the figure, a 9 for use in advance according to the temperature and brightness range.
Lookup tables LUT1 to LUT9 are set. For example, the temperature is Ta to Tb, the brightness is La to
In the range of Lb, the lookup table LUT1 is set. The table changing unit 57 refers to this map and selects a lookup table according to the detection results of the temperature sensor 70 and the optical sensor 80. For example, if the temperature is T
m, when the brightness is Lm, the lookup table L
UT5 is selected.

The LCD driver 56B has an electronic volume 58 and an electronic volume automatic setting section 59. As with the lookup table change described above, the color L
The relationship between the temperature and brightness of the environment using the CD panel and the set value of the electronic volume is set in the map in advance,
The electronic volume automatic setting section 59 refers to this map and sets the set value of the electronic volume 58 so as to maximize the contrast of the color LCD panel according to the detection results of the temperature sensor 70 and the optical sensor 80.

When the set value of the electronic volume 58 changes, the display characteristics of the color LCD panel 20B also change. Therefore, the above-described lookup tables LUT1 to LUT1
The LUT 9 takes into account the set value of the electronic volume 58. FIG. 14 is an explanatory diagram showing an example of the relationship between the setting of the electronic volume 58 and the tone curve.
Now, it is assumed that the temperature and brightness of the use environment of the color LCD panel 20B are constant. As shown in FIG. 14A, when the set value of the electronic volume 58 is changed, the range of the effective drive voltage of the color LCD panel 20B becomes
(See FIG. 22). At this time, the color L
The tone curve is changed as shown in FIG. 14B according to the profile of the transmittance characteristic of the CD panel 20B. Each of these tone curves is similar to the tone curve shown in the first embodiment, and is similar to the color LCD panel 20B.
Is a tone curve having an effect of compensating for the non-linear display characteristics of FIG.

As described above, the color LCD panel 20
For B, the display characteristics change depending on the environmental conditions such as temperature and brightness and the set value of the electronic volume. Therefore, according to the second embodiment, appropriate contrast can be obtained and appropriate image processing can be performed according to the environmental conditions in which the color LCD panel 20B is used. As a result, the display quality of the color LCD panel 20B can be improved.

E. Third Embodiment: FIG. 15 shows a third embodiment of the present invention.
Mobile phone 10C provided with image processing device as embodiment
FIG. 3 is a block diagram showing the configuration of FIG. Except for matters described below, the configuration is the same as that of the second embodiment. Mobile phone 10
C is a color LCD panel 20B as an image display unit
And a system unit 60C. The color LCD panel 20B includes a temperature sensor 70 and an optical sensor 80. The temperature and brightness detected by the temperature sensor 70 and the optical sensor 80 are transmitted to an electronic volume automatic setting unit 59 and a gradation value correction data generation unit 54D described later. Can be

[0099] The system section 60C includes the application program 30, the browser 40, and the image processing module 50C. The image processing module 50C includes:
An image processing unit 52C and an LCD driver 56B are provided. The image processing unit 52C includes a resolution conversion unit 53, an image data correction unit 54C, and a halftone processing unit 55.

The image data correction section 54C includes a gradation value correction data generation section 54D. The tone value correction data generation unit 54D has a function of generating the above-described tone curve. FIG. 16 is an explanatory diagram showing a process of generating a tone curve. First, the display characteristics (the relationship between the input gradation value and the output brightness) of the color LCD panel 20B are specified according to the detection results of the temperature sensor 70 and the optical sensor 80 and the set value of the electronic volume 58 (step S30).
0). This display characteristic is based on the temperature sensor 70, the optical sensor 80
Is stored in the memory in advance, using the detection result of and the set value of the electronic volume 58 as parameters. Next, a desired display characteristic stored in the memory in advance is specified (step S320). Desired display characteristics can be arbitrarily set. For example, the relationship between the input gradation value and the displayed brightness may be set to be linear, or a color LCD may be set.
The setting may be made in consideration of the gamma characteristic of the panel 20. Next, a tone curve is set so as to compensate for the difference between the two (step S340). The image data correction unit 54C
With this gradation value correction data, gradation correction of the image data is performed.

As described above, according to the third embodiment, it is not necessary to previously store a plurality of look-up tables corresponding to the temperature and brightness of the environment in which the color LCD panel 20B is used. Can be suppressed.

F. Fourth Embodiment: FIG. 17 shows a fourth embodiment of the present invention.
Mobile phone 10D provided with image processing device as embodiment
FIG. 3 is a block diagram showing the configuration of FIG. Except for the matters described below, the configuration is the same as that of the first embodiment. The mobile phone 10D is
A color LCD panel 20 as an image display unit and a system unit 60D are provided. The system unit 60D includes the application program 30, the browser 40, and the image processing module 50D. The image processing module 50D includes an image processing unit 52D and an LCD driver 56.
And The image processing unit 52D includes a resolution conversion unit 5
3 and a halftone processing unit 55D. It should be noted that there is no image data correction unit or gradation value correction table for performing gradation correction of image data.

The processing in the halftone processing section 55D will be described. FIG. 18 is an explanatory diagram showing the relationship between the input value (or the correction value) and the recording ratio of the display gradation value CDX. FIG. 18A shows the halftone process of the first embodiment. FIG. 18B shows the halftone process of the fourth embodiment. Here, the recording rate refers to a ratio of pixels occupied in a so-called solid area where a certain gradation value is continuously distributed, that is, when the area is displayed. FIG.
In (a), for example, when the correction value obtained by performing gradation correction on the gradation value of the solid region is 91, the display gradation value CDX =
Pixels 2 and CDX = 3 are generated by being dispersed 50% each. In other words, the correction value is 91
Pixels have a 50% probability of CDX = 2 or CDX = 3
Means to be assigned to

In the first embodiment, as shown in FIG. 18A, the threshold values TH1 to TH6 used for the halftone processing are set almost equally. In the fourth embodiment, as shown in FIG. 18B, the settings of the threshold values TH1 to TH6 are different. These thresholds TH1 to TH6 are set such that the width of the interval is the same as the width of the brightness output for the display gradation value CDX. That is, the brightness that can be output by the color LCD panel 20 is 0 to 100, and the brightness output for the display gradation value CDX = 0, 1, 2, 3, 4, 5, 6, 7 is 0, respectively. , 5,17,37,62,
84, 95, and 100, the threshold values TH1 to TH1
13, 43, 94, 158, 214, 24 as TH6
2 are respectively set. The width of the threshold interval is
It is not necessary that the brightness interval be exactly the same.

According to the fourth embodiment, the two-stage image processing of gradation correction and halftone processing performed in the first embodiment is equivalent to the two-stage image processing, that is, the non-linearity of the display characteristics of the color LCD panel 20 is reduced. Image processing to be compensated can be realized only by halftone processing.

The halftone processing unit 5 of the fourth embodiment
Image processing may be performed by combining 5D and the image data correction unit 54 of the first embodiment. That is, the color L is partially corrected by the gradation correction in the image data correction unit 54.
The non-linear display characteristics of the CD panel 20 may be compensated, and the rest may be compensated by the halftone processing unit 55D.

G. Fifth Embodiment FIG. 19 shows a fifth embodiment of the present invention.
Mobile phone 10E provided with an image processing device as an embodiment
FIG. 3 is a block diagram showing the configuration of FIG. The components other than those described below are the same as those of the second embodiment. The mobile phone 10E is
A color LCD panel 20 as an image display unit and a system unit 60E are provided. The system unit 60E includes the application program 30, the browser 40, and the image processing module 50E. The image processing module 50E includes an image processing unit 52E and an LCD driver 5
6 is provided. The image processing unit 52E includes a resolution conversion unit 53, a halftone processing unit 55E, and a threshold value changing unit 57.
E.

The threshold changing unit 57E has a plurality of threshold tables according to the environment (temperature, brightness) used and the setting of the electronic volume 58. In the threshold table,
Threshold values TH1 to TH6 used for halftone processing are stored. The threshold changing unit 57E selects an optimum threshold table according to the detection results of the temperature sensor 70 and the optical sensor 80. The halftone processing unit 55E performs halftone processing based on the selected threshold value table. In the present embodiment, the threshold changing unit 57E selects an optimum table from a plurality of threshold tables, but each threshold may be set by a predetermined calculation.

According to the fifth embodiment, image processing equivalent to that of the second embodiment can be performed.

Since the image processing apparatus of the present embodiment described above includes processing by a computer, it adopts an embodiment as a computer program for realizing this processing and a recording medium on which the program is recorded. You can also. Further, it is also possible to adopt a mode as a recording medium in which a tone curve used for the image processing of the first and second embodiments is recorded as a gradation value correction table. Such recording media include flexible disks, CD-ROMs, magneto-optical disks, IC cards, RO
M cartridge, punched card, printed matter on which a code such as a barcode is printed, a computer internal storage device (R
Memory such as AM and ROM) and external storage devices,
Various computer readable media are available.

H. Modifications: The embodiments of the present invention have been described above. However, the present invention is not limited to such embodiments at all, and can be implemented in various modes without departing from the gist thereof. It is. For example, the following modifications are possible.

H1. Modification Example 1 In the above embodiment, the present invention was applied to a mobile phone, but the present invention is not limited to this. For example, the present invention can be applied to an electronic device including a liquid crystal display device that displays an image, such as a portable information terminal or a car navigation system.

H2. Modified Example 2: In the above embodiment, a color LCD panel that performs passive matrix driving is used for an image display device. Applicable to: The present invention relates to, for example, a thin film transistor (TFT).
r) and thin film diodes (TFD: Thin Film)
The present invention can also be applied to an active matrix driven color LCD panel using a diode. In the above embodiment, the color LCD driven by the frame thinning method is used.
Although the panel 20 is used, the present invention is also applicable to a color LCD panel driven by a pulse width modulation method.

The present invention is particularly effective when applied to a nonlinear relationship between the input gradation value and the display gradation value, but can also be applied to a case where the display characteristics are linear.
Even in such a case, image quality can be improved by performing gradation correction according to the display characteristics.
The display characteristics to be considered include, for example, a bias in overall brightness, an increase in brightness with respect to an increase in display gradation value, and the number of displayable gradations.

H3. Modification 3 In the above embodiment, the present invention is applied to a liquid crystal display device that performs voltage drive control, but is not limited to this. For example, the present invention can be applied to an LED display device that performs current drive control and an image display device that can perform multi-tone expression of an image by controlling a drive signal.

H4. Modified Example 4: In the above embodiment, the file format of the input image data is the GIF of the 8-bit color table, but the file format of the image data may be, for example, JPEG of the 24-bit RGB color format.

H5. Modification 5 In the first to third embodiments, the halftone process is performed, but the halftone process need not be performed.

H6. Modification 6: In the second embodiment, the gradation value correction table and the electronic volume 5 are set according to the temperature and brightness of the environment in which the color LCD panel 20 is used.
Although the value of 8 is set, it may be set according to either one. Further, a look-up table corresponding to the temperature and brightness of the environment in which the color LCD panel 20 is used and a look-up table corresponding to the set value of the electronic volume 58 are separately prepared, and a two-stage floor using each table is prepared. Tone correction may be performed. Also,
The setting may be made according to the brightness of the backlight of the color LCD panel 20 or the on / off state.

H7. Modification 7: In the above embodiment, the mobile phone as the image display device includes the image processing device. However, the image processing device and the image display device may be independent. For example, the server SV storing the image data may include some or all of the image processing device of the present invention. For example, when transmitting image data to the mobile phone 10, the server SV may perform the processing up to the gradation value correction of the image processing shown in FIG. 2, and the mobile phone may perform halftone processing. The server SV may perform up to halftone processing. The above processing may be performed by the server SV when saving the uploaded image data.

Further, a part or all of the image processing apparatus of the present invention may be provided in a user's computer or the like. That is, before uploading the image data to the server SV, the processing up to the gradation correction may be performed by the user's computer or the like, or the processing up to the halftone processing may be performed.

By doing so, the display characteristics (corresponding to the model of the mobile phone in the embodiment) of the image display device to be displayed are specified, and the image quality of the display image is improved according to the display characteristics. The image data can be corrected in advance.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of a mobile phone 10 including an image processing apparatus according to a first embodiment of the present invention.

FIG. 2 is a flowchart of an image processing routine performed by an image processing module 50;

FIG. 3 shows an 8-bit palette index color of 24
FIG. 3 is an explanatory diagram showing a color table for converting to a bit RGB color format.

FIG. 4 is an explanatory diagram showing a tone curve representing a relationship between a tone value DXR of input image data for R (red) and a tone value DXr of corrected image data.

FIG. 5 is a tone value correction table LUT that represents a tone curve for R (red) in a table.

FIG. 6 is a flowchart of a halftone processing routine according to the present embodiment.

FIG. 7 is an explanatory diagram illustrating an example of a dither matrix.

FIG. 8 is an explanatory diagram illustrating an effect of image processing according to the present embodiment.

FIG. 9 is an explanatory diagram illustrating an effect of image processing according to the present embodiment.

FIG. 10 is a block diagram illustrating a configuration of a mobile phone 10A including an image processing device according to a modification of the first embodiment.

FIG. 11 shows R recorded in a second gradation value correction table.
The first correction value DXr and the second correction value
FIG. 8 is an explanatory diagram showing a tone curve representing a relationship with a correction value DXr ′.

FIG. 12 is a block diagram illustrating a configuration of a mobile phone 10B including an image processing device according to a second embodiment of the present invention.

FIG. 13 is an explanatory diagram showing a map representing a relationship between a temperature and brightness of an environment using a color LCD panel and a lookup table to be used.

FIG. 14 is an explanatory diagram showing an example of the relationship between the setting of the electronic volume 58 and the tone curve.

FIG. 15 is a block diagram illustrating a configuration of a mobile phone 10C including an image processing device according to a third embodiment of the present invention.

FIG. 16 is an explanatory diagram illustrating a generation process of a tone curve.

FIG. 17 is a block diagram illustrating a configuration of a mobile phone 10D including an image processing device according to a fourth embodiment of the present invention.

FIG. 18 shows input values (or correction values) and display gradation values CDX.
FIG. 4 is an explanatory diagram showing a relationship with a recording rate of the image.

FIG. 19 is a block diagram illustrating a configuration of a mobile phone 10E including an image processing device as a fifth embodiment of the present invention.

FIG. 20 is an explanatory diagram showing a state in which data of 256 gradations is allocated to 8 gradations.

FIG. 21 is an explanatory diagram showing a voltage-transmittance characteristic (VT characteristic) of an LCD panel.

FIG. 22 is an explanatory diagram illustrating adjustment of display contrast of an LCD panel using an electronic volume.

[Explanation of symbols]

10, 10A, 10B, 10C, 10D, 10E: Mobile phone 20: Color LCD panel 30: Application program 40: Browser 50, 50A, 50B, 50C, 50D, 50E: Image processing module 52, 52A, 52B, 52C, 52D , 50E image processing unit 53 resolution conversion unit 54, 54C image data correction unit 54D gradation value correction data generation unit 55, 55D, 55E halftone processing unit 56, 56A LCD driver 57 table change unit 57E Threshold change section 58 Electronic volume 59 Electronic volume automatic setting section 60, 60A, 60B, 60C, 60D, 60E System section 70 Temperature sensor 80 Optical sensor 541 First image data correction section 542 Second image Data correction unit

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) G09G 3/20 641 G09G 3/20 641H 5C079 641P 5C080 642 642F 650 650M H04N 1/407 H04N 9/64 Z 1 / 46 1/46 Z 1/60 1/40 D 9/64 101E F-term (reference) 2H093 NA55 NC13 NC55 NC56 NC57 NC63 NC65 ND02 ND06 ND20 ND24 ND39 5B057 AA20 CA01 CA08 CA12 CA16 CB01 CB08 CB12 CB16 CC01 CD07 CE11 CH01 CH07 DA16 5C006 AA13 AA22 AF44 AF46 AF47 BB11 BC16 FA29 FA56 5C066 AA01 AA11 EA11 EB01 EC06 GA01 GA32 HA02 KE07 KE11 KE16 KM01 KM13 KP02 5C077 LL04 LL19 MP01 MP08 NN08 PP15 PP32. MA17 NA05 PA05 5C080 AA10 BB05 CC03 DD03 DD30 EE29 EE30 FF09 GG02 JJ02 JJ05 JJ06 JJ07 KK 47

Claims (31)

[Claims] 1. An image processing apparatus for performing predetermined image processing on image data to generate data to be supplied to an image display device, wherein the image display device performs gradation display by a frame thinning method. A liquid crystal display device in which the number of display gradations that can be displayed in pixel units is smaller than the number of gradations of the image data; the image processing device comprises: an input unit for inputting the image data; A color reduction processing unit that sets a display gradation value that can be displayed by the liquid crystal display device on a pixel-by-pixel basis, wherein the color reduction processing unit calculates the gradation value assigned to the display gradation value. An image processing apparatus that performs the setting so that a range is narrower than a half tone, at least one of a high tone and a low tone. 2. The image processing apparatus according to claim 1, wherein the image data correction unit performs a gradation correction for suppressing a gradation distribution in a halftone region and increasing a distribution in a low gradation region and a high gradation region. An image processing apparatus comprising: 3. The image processing apparatus according to claim 1, further comprising a storage unit configured to store a relationship between a gradation value of the input image data and a corrected gradation value, and refer to the storage unit. And an image processing device including an image data correction unit for correcting the gradation value. 4. An image processing apparatus for performing predetermined image processing on image data to be displayed on an image display device and generating data to be supplied to the image display device, wherein the image display device includes The number of display gradations that can be expressed for each image is smaller than the number of gradations of the image data, and the brightness output for the display gradation value is stepwise, and the interval between the display gradation values is non-linear. An apparatus having display characteristics, wherein in consideration of the non-linearity of the display characteristics, in the gradation distribution of the input image data, the gradation distribution corresponding to the wide area is increased, and the distance is narrow. An image data correction unit that performs a gradation correction for suppressing a gradation distribution corresponding to the region and generates a correction value; and divides a gradation range of the correction value into a predetermined number of sections, and calculates the correction value in the section. According to the prescribed rules A color reduction processing unit that performs color reduction processing by assigning to the display gradation value. 5. The image processing apparatus according to claim 4, wherein the predetermined number of sections is a section in which a gradation range of the correction value is divided into equal ranges. 6. An image processing apparatus for performing predetermined image processing on image data to be displayed on an image display device and generating data to be supplied to the image display device, wherein the image display device includes The number of display gradations that can be expressed for each image is smaller than the number of gradations of the image data, and the brightness output for the display gradation value is stepwise, and the interval between the display gradation values is non-linear. An apparatus having display characteristics, wherein a gradation range of gradation values of the image data is divided into sections having a width corresponding to the display characteristics, and gradation values in the sections are displayed according to a predetermined rule. An image processing apparatus including a color reduction processing unit that performs color reduction processing by assigning values to values. 7. The image processing apparatus according to claim 1, wherein the color reduction processing unit performs distributed halftone processing. 8. The image processing apparatus according to claim 7, wherein the color reduction processing unit performs the distributed halftone processing only when the image data is of a predetermined type. 9. The image processing device according to claim 4, wherein the image display device is a liquid crystal display device that is used in a mobile phone and performs gradation display by a frame thinning method.
Image processing device. 10. The image processing apparatus according to claim 4, wherein the image data correction unit further suppresses a gradation distribution in a halftone region and increases a distribution in a low gradation region and a high gradation region. An image processing device that performs tone correction. 11. The image processing apparatus according to claim 4, wherein the image data correction unit stores a relationship between a gradation value of the input image data and a corrected gradation value. And an image processing device for correcting the gradation value with reference to the storage unit. 12. The image processing apparatus according to claim 11, wherein a plurality of the storage units are prepared according to a condition affecting display characteristics of the image display device, and the storage unit is configured to store the storage unit according to the condition. An image processing apparatus, comprising: a storage unit changing unit for changing a unit. 13. The image processing device according to claim 12, wherein the condition is a temperature of an environment in which the image display device is used. 14. The image processing apparatus according to claim 12, wherein the condition is a brightness of an environment in which the image display device is used. 15. The image processing device according to claim 12, wherein the image display device is a liquid crystal display device having a backlight, and the condition is brightness of the backlight. 16. The image processing device according to claim 12, wherein the condition is a set value of a contrast adjuster for adjusting a display contrast of the image display device. 17. The number of display gradations that can be expressed for each pixel is smaller than the number of gradations of the image data, the brightness output for the display gradation value is stepwise, and the interval is An image processing apparatus that performs predetermined gradation correction on image data to be displayed on an image display device having a non-linear display characteristic having a wide and narrow range, wherein a relationship between a gradation value of the image data and the brightness is determined. A first storage unit that stores the parameter value in association with a predetermined parameter value; a second storage unit that stores a predetermined relationship between the gradation value and the brightness set in advance; Data representing the relationship between the tone value of the image data and the tone value of the corrected image data so as to compensate for the difference between the two based on the relationship specified by the parameter value and the desired relationship. Data generation unit that generates An image processing apparatus comprising: an image data correction unit configured to correct a gradation value of the input image data with reference to the generated data. 18. An image processing apparatus for performing predetermined image processing on image data to be displayed on an image display device and generating data to be supplied to the image display device, comprising: A storage unit that stores in advance a relationship set based on the display characteristics of the image display device; an image data correction unit that performs tone correction of the image data based on the relationship; A color reduction processing unit configured to reduce the number of colors to the number of gradations that can be displayed on the image display device. 19. The image processing apparatus according to claim 18, wherein the color reduction processing unit performs distributed halftone processing. 20. The image processing apparatus according to claim 18, wherein a plurality of said storage means are prepared according to a condition affecting display characteristics of said image display device, and said storage means is stored according to said condition. An image processing apparatus, comprising: a storage unit changing unit for changing a unit. 21. A gradation display is performed by a frame thinning-out method, and a predetermined number of display gradations that can be displayed in a pixel unit are smaller than the number of gradations of the image data. An image processing method for performing image processing and generating data to be supplied to the liquid crystal display device, comprising: (a) specifying display characteristics of the liquid crystal display device to be displayed; and (b) the liquid crystal display device. Pixel based on the grayscale value so that the range of the grayscale value of the image data assigned to the display grayscale value that can be displayed is narrower than at least one of high grayscale and low grayscale than halftone. Setting the display gradation value for each image processing method. 22. The number of display gradations that can be expressed for each pixel is smaller than the number of gradations of the image data, the brightness output for the display gradation value is stepwise, and the interval is An image processing method for performing predetermined image processing on image data to be displayed on an image display device having a non-linear display characteristic having a wide and narrow area, and generating data to be supplied to the image display device, wherein (a) (B) determining a display characteristic of an image display device to be displayed; and (b) considering a non-linearity of the display characteristic, in a gradation distribution of input image data, a floor corresponding to a region having a wide interval. Performing a tone correction for increasing a tone distribution and suppressing a tone distribution corresponding to the area where the interval is narrow, and generating a correction value;
(C) performing a color reduction process by dividing the gradation range of the correction value into a predetermined number of sections and assigning the first correction value in the section to the display gradation value according to a predetermined rule; An image processing method comprising: 23. The number of display gradations that can be expressed for each pixel is smaller than the number of gradations of the image data, the brightness output for the display gradation value is stepwise, and the interval is An image processing method for performing predetermined image processing on image data to be displayed on an image display device having a non-linear display characteristic having a wide and narrow area, and generating data to be supplied to the image display device, wherein (a) (B) dividing the gradation range of the gradation value of the image data into sections having a width corresponding to the display characteristics, and a floor within the section; Performing a color reduction process by assigning a tonal value to the display gradation value in accordance with a predetermined rule. 24. The number of display gradations that can be expressed for each pixel is smaller than the number of gradations of image data, the brightness output for the display gradation value is stepwise, and the interval between the brightnesses is stepwise. A method for generating data used for performing predetermined gradation correction on image data to be displayed on an image display device having a non-linear display characteristic having a wide and narrow area, comprising: Specifying a relationship between a tone value and the brightness; (b) setting a desired relationship between the tone value and the brightness; and (c) determining the relationship specified in the step (a). And data representing the relationship between the tone value of the image data and the tone value of the corrected image data so as to compensate for the difference between the two based on the relationship set in the step (b). And generating. 25. An image processing method for performing predetermined image processing on image data to be displayed on an image display device and generating data to be supplied to the image display device, comprising: A step of storing in advance a relation set based on display characteristics of the image display device; a step of performing gradation correction of the image data based on the relation; and a step of converting the corrected image data into the image. Reducing the number of colors to the number of gradations that can be displayed on the display device. 26. A gradation display is performed by a frame thinning-out method, and a predetermined number of display gradations that can be displayed in pixel units are smaller than the gradation number of the image data. A computer program for performing image processing, comprising: a function of specifying display characteristics of the liquid crystal display device to be displayed; and a gradation value of the image data assigned to a display gradation value that can be displayed by the liquid crystal display device. A function of setting the display gradation value for each pixel based on the gradation value so that the range is at least one of a high gradation and a low gradation, and narrower than a halftone. Computer programs. 27. The number of display gradations that can be expressed for each pixel is smaller than the number of gradations of the image data, the brightness output for the display gradation value is stepwise, and the interval is A computer program for performing predetermined image processing on image data to be displayed on an image display device having a non-linear display characteristic having a wide and narrow area, a function of specifying display characteristics of the image display device to be displayed, In consideration of the non-linearity of the display characteristics, in the gradation distribution of the input image data, while increasing the gradation distribution corresponding to the region with a large interval, the gradation distribution corresponding to the region with a small interval is increased. A function of performing gradation correction to be suppressed, and a gradation reduction range by dividing the gradation range of the correction value into a predetermined number of sections and assigning the correction values in the section to the display gradation values according to a predetermined rule. A computer program that allows a computer to implement 28. The number of display gradations that can be expressed for each pixel is smaller than the number of gradations of image data, the brightness output for the display gradation value is stepwise, and the interval is A computer program for performing predetermined image processing on image data to be displayed on an image display device having a non-linear display characteristic having a wide and narrow area, a function of specifying display characteristics of the image display device to be displayed, The color reduction process is performed by dividing the gradation range of the gradation values of the image data into sections having a width corresponding to the display characteristics and assigning the gradation values in the sections to the display gradation values according to a predetermined rule. The functions to be performed, and a computer program that causes the computer to realize. 29. The number of display gradations that can be expressed for each pixel is smaller than the number of gradations of the image data, the brightness output for the display gradation value is stepwise, and the interval is A computer program for generating data used for performing predetermined tone correction on image data to be displayed on an image display device having a non-linear display characteristic having a wide and narrow range, wherein the tone value of the image data A function for specifying a relationship between the brightness and the brightness; a function for setting a relationship between a desired gradation value and the brightness; and a function based on the specified relationship and the set relationship. And a function of generating data representing a relationship between the tone value of the image data and the tone value of the corrected image data so as to compensate for the difference. 30. A recording medium on which the computer program according to claim 26 is recorded in a computer-readable manner. 31. The number of display gradations that can be expressed for each pixel is smaller than the number of gradations of the image data, the brightness output for the display gradation value is stepwise, and the interval is A computer-readable recording medium on which a computer program for performing predetermined image processing on image data to be displayed on an image display device having a non-linear display characteristic having a wide and narrow area is provided. A recording medium on which data representing the relationship between the gradation value of the image data input to the image processing apparatus and the gradation value of the corrected image data is recorded.